Hypertrophic cardiomyopathy is found in 1:500 people. In patients with hypertrophic obstructive cardiomyopathy (HOCM), left ventricular outflow tract obstruction (present in 25% of patients with HOCM) can lead to significant symptoms, reduction in functional capacity, angina, syncope, and sudden death. The obstruction is dynamic and is usually due to a combination of septal muscular bulging and systolic anterior motion of the anterior mitral valve leaflet (SAM)—the latter results from a Venturi effect rather than from intrinsic mitral valve disease. In addition to contributing significantly to LVOT obstruction, SAM can also lead mitral regurgitation in the setting of HOCM.
SAM also occurs in patients post mitral valve surgical annuloplasty where an annuloplasty ring has resulted in excess longitudinal apical displacement of the anterior leaflet tip (redundant) and subsequent SAM in the absence of septal hypertrophy. LVOT obstruction secondary to SAM is also recognized to occur in patients (often elderly) with a sigmoid intraventricular septum in the absence of HOCM.
Methods of treating SAM in patients with HOCM include surgical septal myectomy and catheter based alcohol septal ablation.
Surgical septal myectomy is an open heart operation performed to relieve symptoms in patients who remain severely symptomatic despite medical therapy. It has been performed successfully for more than 25 years. Surgical septal myectomy uniformly decreases left ventricular outflow tract obstruction and improves symptoms, and in experienced centers has a surgical mortality of less than 1%, as well as 85% success rate. It involves a median sternotomy (general anesthesia, opening the chest, and cardiopulmonary bypass) and removing a portion of the interventricular septum. Surgical myectomy is focused just on the subaortic LVOT section of the septum, to increase the size of the outflow tract to reduce Venturi forces may be inadequate to abolish systolic anterior motion (SAM) of the anterior leaflet of the mitral valve. With this limited sort of resection the residual mid-septal bulge still redirects flow posteriorly and SAM still persists. It is only when the deeper portion of the septal bulge is resected that flow is redirected anteriorly away from the mitral valve, abolishing SAM. With this in mind, a modification of the Morrow myectomy termed extended myectomy, mobilization and partial excision of the papillary muscles has become the excision of choice. In selected patients with particularly large redundant mitral valves, anterior leaflet plication may be added to complete separation of the mitral valve and outflow. Complications of septal myectomy surgery include possible death, stroke, AV nodal conduction block and requirement for permanent pacemaker, arrhythmias, infection, incessant bleeding, septal perforation/defect.
Transcatheter alcohol septal ablation, introduced by Ulrich Sigwart in 1994, is a percutaneous technique that involves injection of alcohol into one or more septal branches of the left anterior descending artery. This is a technique with results similar to the surgical septal myectomy procedure but is less invasive, since it does not involve general anesthesia and opening of the chest wall, pericardium, aorta or heart (which are done in a surgical septal myomectomy with mitral valve modification). In a select population with symptoms secondary to a high outflow tract gradient, alcohol septal ablation can reduce the symptoms of HCM. In addition, older individuals and those with other medical problems, for whom surgical myectomy would pose increased procedural risk, would likely benefit from the lesser invasive septal ablation procedure. When appropriate coronary septal artery anatomy exists, alcohol septal ablation induces a controlled heart attack, in which the portion of the interventricular septum that involves the left ventricular outflow tract is infarcted and will contract into a scar. The potential complications of this procedure include death, stroke, larger extensive myocardial infarction, AV nodal conduction block with requirement for permanent pacemaker, infection, and arrhythmias.
US2008/086164 (Rowe) discloses heart implants for treatment of globular left ventricle, which is the opposite to hypertrophic cardiomyopathy with LVOT obstruction (HOCM), by implanting a device configured to elongate the left ventricle to restore a conical shape and reverse widening and rounding of the left ventricle. Such a device could potentially make LVOT obstruction worse in the context of HOCM.
US2007/0061010 (Hauser) discloses a solution for mitral annular dilation and resultant functional mitral regurgitation which occurs in left ventricular dilation (i.e. in dilated cardiomyopathy rather than hypertrophic cardiomyopathy) that involves implanting a device configured to compress the mitral valve annulus directly or indirectly to reduce mitral annular dilation. Such a device would not prevent leaflet and sub-valvular apparatus from migrating into the LVOT in systole in patients with HOCM.
US2014/0100596 (Rudman) describes methods for reducing blood volume in the left atrial appendage by implanting a volume-adding member having an impermeable membrane. Such a device would have no effect on HOCM.
It is an object of the invention to overcome at least some of the above-referenced problems.